Can someone give more details about how vzctl snapshots and ploop snapshots work together? Especially deleting and merging snapshots. I just stumled up sutiation when I have created snapshots with vzctl, then merged them with ploop, but vzctl still shows them. How do I resolved such condition? How do I merge snapshots with vzctl?

So vzctl only has snapshot delete function which deletes snapshot, if I delete snap2, then my VE will return to state2 and state2 will become current and changes from state3 will be lost? I.e. deleting snapshot reverts to previous state or merges two adjacent states discarding snapshot
With ploop it's more obvious that when I do ploop merge snap2, then state2 and state3 will be merged, snap 2 removed and new current state will be state2+3. Then ploop merge snap1 and it will merge state1 and state2+3 resulting in only one state, i.e. state3(or 1+2+3) becomes the only state.